MPEG media transport (MMT) as a standardized data transmission technology defines formats for transporting coded data. According to MMT, a receiving apparatus has a feature that enables it to issue an automatic repeat request (ARQ), whereby re-transmission of an MMT packet that was lost during transmission can be requested.
According to the existing packet re-transmission scheme, when a transmitted packet is lost, a receiving apparatus determines whether to send an ARQ feedback message to a transmission apparatus (e.g., a server), assuming that said receiving apparatus already has information regarding the round-trip time (RTT). Said receiving apparatus takes into consideration the information it has regarding the RTT, and then sends out a request for re-transmission of the lost packet. In other words, considering the fact that the RTT is an estimation of the time it will take to receive the lost packet, the receiving apparatus may still send the ARQ feedback message even when the re-transmitted packet has arrived to the receiving apparatus after the RTT if it is determined that the received packet can be effectively utilized; otherwise, the receiving apparatus may not send out the ARQ feedback message.
FIG. 1 is a diagram illustrating a conventional method, oriented to a receiving entity, for re-transmitting a packet.
Referring to FIG. 1, in a case where a packet, which is referred to as ‘packet 2’, was transmitted from a transmission apparatus 110 but has been lost, a receiving apparatus 120 may determine whether to request re-transmission of packet 2 by taking into consideration its RTT. The receiving apparatus 120 will send out an ARQ feedback message to request re-transmission of packet 2 if it is determined that the re-transmitted packet 2 that arrives at the receiving apparatus 120 after the RTT can be effectively used; otherwise, the receiving apparatus 120 does not send out the ARQ feedback message. FIG. 1 illustrates an example in which the requested packet 2 arrives at the receiving apparatus 120 after the RTT has elapsed since a request was made for re-transmission of said packet; the re-transmitted packet can be effectively utilized only when its arrival time does not exceed Td(2).
As such, in the conventional re-transmitting method, a packet may be useful if the receiving apparatus has obtained an estimation of the RTT. However, in a media transport system environment based on the real-time transport protocol (RTP) and MMT protocol, it is not a receiving apparatus but a transmission apparatus that obtains an estimate of the RTT. Therefore, the conventional packet re-transmission method based on RTT estimations by the receiving apparatus cannot be applied to an MMT-based service environment.